Erosion and solid transport is a tricky and complex problem that negatively affects natural and urban environments. In Algeria, the effects of this phenomenon are apparent; their impact is no less devastating in the long term than the other spectacular catastrophic phenomena that can be observed. Sixty-five large dams in Algeria are threatened by the reduction of 62% of their storage capacity because of the siltation problem (ANBT) (National Agency for Dams and Water Transfers). The main objective of this work is the evaluation of the impact of the erosion phenomenon on Bechar watershed which is in an area characterized by an arid climate. The universal soil loss equation was used. This model is based on the combination of the five factors (erosivity, erodibility, topography, vegetation cover and support practices) that directly influence this phenomenon. Analytical hierarchy process is used to give a weighting value of each factor according to its degree of influence on the phenomenon. The sediment delivery ratio is calculated to determine the amount of soil that will arrive at the outlet of the watershed and contribute to the storage structures siltation. The obtained results will undoubtedly help decision makers to understand the threat of erosion degree in the study area in order to better take the necessary measures to face this issue.

In this study, we evaluate the soil erosion and solid transport in the oued Mekerra watershed in north-west Algeria. The study area is subject to a semi-arid climate characterized by irregular rainfall and showers, which are often accompanied by significant floods. These floods of large volumes transport large amounts of solid input to the Sarno dam, which is in the outlet of oued Mekerra. Therefore, the water storage capacity of this dam is gradually decreasing, and it might reach the volume of dead water. For this study, we utilized the hydrometric database provided by the National Agency of Water Resources (ANRH). The operating period was 24 years, from 1988 to 2012. This period was extended by classic regression to 65 years, which allowed extracting a series of annual maximum instantaneous flow rates (Q IXA ) and subsequently quantified the sediment yield during floods. The specific degradation mean created by the 11 floods was quite high, in the order of 20 t km 2 year −1 . The highest value of solid contribution was observed during the floods of October 2000 (250,000 t), and the value of liquid contribution was 7,151,608 m 3 . The extracted results from the analysis of the graphs of concentration as a function of the liquid flow (C = f′(Q l )) showed four types of hysteresis curves: clockwise loop, counterclockwise loop, shape of eight, and straight line curve. Class II (clockwise loop) was the dominant class in the four events, namely the floods that occurred on 09/22/1992, 09/21/1998, 09/27/1999, and the 08/24/2002. From these results, the water resource sector managers could formulate various methods for protection from floods and against the risk of sedimentation in storage structures.

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a b s t r a c tThis work is based on the characterization of the physico-chemical parameters in the groundwater of the Bechar-Kenadsa region in southwest Algeria. To achieve this goal, we have collected a database of a water sampling survey that has been done by the National Hydric Resources Agency (ANRH) of the different water points located in the study area according to recognized standards for the collection and analysis protocols of water samples. We extracted the pH, EC, TDS, Ca -parameters, we used these physical and hydro chemical characteristics to evaluate the parameters of the sodium content (Na %), Kelly's rate and permeability index. The results showed that just small portion of the groundwater was drinkable. We also used diagrams like Piper's to distinguish that the main water quality is of the Mg-Cl-SO 4 class. The Durov's diagram helped us to know that most of this water is concentrated in the area, of magnesium-dominance, characterized by two main classes of water (Mg-Cl-SO 4 and Mg-Ca-Cl-SO 4 ). The Gibbs diagram was used to assess the mechanisms controlling the chemistry of water. We noticed that the quality of the water was influenced by the precipitation process in the first row. According to the Wilcox diagram, it was noted that most of groundwater in the study area is characterized by high salinity under three main classes (C4-S1, C4-S2 and C4-S3). We can than conclude that the groundwater in the study area is of poor quality for drinking and irrigation and requires serious treatment to be exploited.